CULTURAL HERITAGE AND SEISMIC RISK: SOME EUROPEAN EXPERIENCES

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1 Strasbourg, 7 December 2008 AP/CAT (2008) 56 Or. E. EUROPEAN AND MEDITERRANEAN MAJOR HAZARDS AGREEMENT (EUR-OPA) CULTURAL HERITAGE AND SEISMIC RISK: SOME EUROPEAN EXPERIENCES Published in Risk Wise on the occasion of the 2008 Davos International Disaster and Risk Conference Author: Francesc Pla, European and Mediterranean Major Hazards Agreement EUR-OPA, Council of Europe

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3 3 Cultural heritage is a key element of the history and identity of societies, contributing to their economy and well being. Disaster reduction, as a tool of sustainable development, concerns not only the prevention of loss of lives and property, but also the protection of cultural assets and the environment from natural or technological hazards. Founded in 1949, the Council of Europe with its 47 member states seeks to develop common and democratic principles throughout Europe, based on the protection of individuals, democracy and the rule of law. Its main tasks include achieving a greater unity between its members to find common solutions to the challenges facing European society. Over the last 20 years, the Council of Europe has been promoting the reduction of the vulnerability of ancient buildings and historical settings from earthquakes and other risks through its European and Mediterranean Major Hazards Agreement (EUR-OPA). EUR-OPA currently counts 25 member states, and has served since 1987 as a platform for cooperation between European and Southern Mediterranean countries in the field of major natural and technological disasters. Its field of action covers the knowledge of hazards, risk prevention, risk management, post-crisis analysis and rehabilitation. EUR-OPA also counts a network of 25 specialised centres, some of which develop projects and activities on cultural heritage and risks: more than 60 seminars, courses, round tables and workshops have been held over the years. Four centres of the EUR-OPA network have been focusing much of their attention on this subject: these are the European University Centre for Cultural Heritage (Ravello, Italy), the European Centre for Prevention and Forecasting of Earthquakes (Athens, Greece), the European Centre on Urban Risks (Lisbon, Portugal) and the European Centre on Vulnerability of Industrial and Lifeline Systems (Skopje, «the former Yugoslav Republic of Macedonia»). Learning from the past It is a fact that it is impossible to completely protect a construction against seismic force, which is sometimes beyond the limits of human capabilities. However, all over the Mediterranean, many historical monuments and traditionally constructed buildings and settlements exist, and for hundreds of years these have repeatedly survived seismic action, even in areas of particularly high seismic risk. Such a historical experience could and should be studied in order to identify possible aseismic techniques already used in the past, which have proved to be efficient and can therefore be reused or updated on ancient buildings and settlements. Learning from monuments Trying to identify native techniques used in past times to increase resilience of monuments (such as churches or palaces) seems an obvious course, as restoration techniques mainly attempt to keep the actual building as close as possible to its original configuration due to its clear historical value. Furthermore, many of those monuments are nowadays managed by public authorities (local, regional or national) which care about their public access as touristic facilities and can adopt quite sophisticated techniques and materials to protect them from future events. The European Centre for Prevention and Forecasting of Earthquakes, in Athens, has devoted a large part of its recent activities to improving the classification and manipulation of data concerning the present status of Hellenic region monuments that actually suffered past impacts and the extend of such impacts. A second step is then to focus on the intrinsic structural properties that protected them from the successive disasters they suffered. After preliminary work to identify typical structural systems related to seismic vulnerabilities and response, a more systematical Digital Database is underway. This information will be useful to prepare guidelines on principals and criteria for

4 4 mitigating the vulnerabilities of monuments through structural restoration that is adapted to each typical structural system, and which takes into account structural properties concerning their foundation aspects (such as topography effects, soil movements, action of underground water), that are generally ignored in the usual aseismic codes. Learning from traditional constructions Cultural heritage cannot be reduced to monuments: buildings that have survived also include many non-monumental ones, such as traditionally constructed housing or settlements. In those cases, the previous two-step methodology could also be used in order to identify the good practices of the past in terms of construction. However, their possible resilience to previous disasters turns out to be more complex: records on previous disasters they suffered are generally less systematic due precisely to their absence of symbolic value for past generations. The European University Centre for Cultural Heritage in Ravello, Italy, has developed an active effort in that field, both in Italy and with international partners. As the use of such buildings evolved and their (mostly private) ownership has changed over time, they may have suffered more successive adaptations than monuments. After having identified traditional building techniques for disaster resilience (but also potential conflicts with modern techniques applied to such buildings), the work has emphasized the role of other factors such as associated land usage or maintenance habits, leading to the wider concept of local culture. Thus, over many years the centre has developed a course to promote the rediscovery and adaptation of accurate traditional techniques as preventive measures against earthquakes, and to diffuse that knowledge among professionals such as architects and urban planners, and authorities that can support such local reinforcement projects. Preparing the future The approach presented above was mainly based on archaeological and historical works and thus mostly relies on the pre-existence of significative data on their historical resilience to disasters. As already pointed out for non monumental buildings, such prerequisites may be difficult to fulfil in some cases and more specially for quite recent monuments, for which historical buildings where interaction is crucial. Simulation approaches have been presented to better deal with such specificities. Focusing on individual monuments The first approach is to concentrate on a specific monument and study its possible resilience to a potential event without reference to previous similar events. To do so, an experimental approach has to be applied, simulating the potential impact on it of different earthquakes. Obviously, such an approach has to rely either on purely numerical calculations or on experiments on associated scale models. The adequacy in specific cases of various reinforcement measures to mitigate seismic effects can then also be tested along the same lines. The European Centre on Vulnerability of Industrial and Lifeline Systems in Skopje is involved in the international project PROHITECH (within the FP6 of the European Commission) to develop suitable methodologies for the use of reversible mixed technologies in the seismic protection of existing constructions, with particular emphasis on buildings of historical and artistic interest. Such buildings cover a wide and diversified range of structural categories such as masonry reinforced concrete buildings and some steel constructions needing to be fitted with adequate aseismic provisions. Part of the activities focus on analysing four models, each representing a characteristic cultural heritage: an Islamic mosque, a Gothic cathedral, a Byzantine church and a Greek temple. The applied methodology includes: 1. In situ measurements of dynamic characteristics of the historical monument

5 5 2. Shaking table tests of original and strengthened models constructed in 1/10 scale 3. Based on the test results, a proposal for the implementation of strengthening measures. Dealing with aggregates of historical buildings If the previous approach is extremely useful, it turns out to be quite reductive when the ancient building is in fact embedded within a more complex network of other ancient and modern buildings. Historical buildings designed prior to the introduction of reasonable earthquake requirements into building codes, buildings with relatively low resistant structures and more recent ones built after major earthquakes can coexist in aggregates, and will determine different responses according to their specificities. The European Centre on Urban Risks in Lisbon has developed a study to forecast the possible effect of various earthquakes on the historical centre of Lagos, in the Algarve region of Portugal. After characterizing the building area through an enquiry carried out to obtain experimental evaluations of building frequency, the seismic analysis of the building stocks behaviour must be determined taking into consideration previous studies on source locations, soil effects, past seismicity, typologies and spatial aggregations. This work has made it possible to characterize the exposed vulnerability of the aggregates, and the number of homeless and injured people, which is calculated by a percentage of the number of collapsed buildings with several damages (according to their frequencies and site location, for intensities of seven to ten). Policy decision-makers and populations can then design a more efficient emergency plan based on the different seismic scenarios and promote some complementary actions (including educational ones) to assure the minimization of damages. Future challenges In the future, work on cultural heritage and risk under the EUR-OPA Agreement will also have to address an additional challenge: the specific impact of climate change on risks via its possible consequences on cultural heritage. Even if climate change essentially affects meteorological risks and apparently has no impact on seismic risk itself, the ageing of the structures and their wearing out due to various causes (such as humidity, groundsettlements or pollution) make historical structures much more vulnerable than modern ones, and in particular with respect to seismic risk.